1. Field of the Invention
The invention relates to a method of setting the folding-nip width of a plurality of pairs of folding rollers which are provided on a folding machine.
2. Description of the Related Art
DE 298 20 796 U1 discloses a folding machine which has a plurality of pairs of folding rollers which are arranged one behind the other in the sheet-passage direction and between which one sheet is guided through in each case. One folding roller of the first pair of folding rollers is arranged in a stationary manner, while the other folding roller is arranged in an adjustable manner in order to form a folding nip with the other folding roller of the corresponding pair of folding rollers. The adjustable folding rollers are prestressed in the direction of the stationary roller in each case by a prestressing device. Arranged on the feed table of the known folding machine is a thickness-measuring device, which measures the thickness of a first passing sheet which is fed to the first pair of folding rollers. The measured value determined is passed on to a process computer. There, with a respective folding layout being taken into account, the necessary folding-nip widths are calculated. Thereafter, the actuating drives are actuated, in order to adjust the adjustable folding rollers, until actual values of position indicators correspond to the desired values which have been calculated. Corrections may be carried out both via a keyboard and via manual spindle drives, which act in parallel with the motor drives and also act on the position indicators.
Determining the necessary folding-nip width by computer is problematic because, in addition to the sheet thickness and the tolerances thereof, the setting values also have to take account of air inclusions, the sheet compression, the roller wear and the roller contamination (applications of ink and powder).
In the case of a further apparatus, which is known from U.S. Pat. No. 4,125,254, first of all all the folding-nip widths are set to zero. Then, a sample sheet is guided through the folder, as a result of which the adjustable folding rollers are deflected and arrested in this deflected position. Corrections to the folding-nip width, however, are not possible in the case of this folding machine, with the result that the operation of setting the folding-roller nip is not practicable.
The object of the invention is to provide a method of setting the folding-nip width of a plurality of pairs of folding rollers by means of which the folding-nip width can be automatically set, and corrected, in a straightforward and precise manner.
This object is achieved according to the invention by a method of setting a folding-nip width of a plurality of pairs of folding rollers which are provided on a folding machine, each pair of folding rollers including at least one adjustable folding roller, comprising the following steps:
the two folding rollers of said pairs of folding rollers are brought into contact with one another,
a sheet is passed between said two folding rollers of said pairs of folding rollers, whereby said at least one adjustable folding roller moves in relation to the other, so that a folding nip is formed, a value corresponding to said folding-nip width being detected for each pair of folding rollers as said sheet is passed therebetween, and
said folding-nip widths of said pairs of folding rollers are set by adjustment of said at least one adjustable folding roller by means of a drive, which is connected kinematically thereto, based on the corresponding detected values which have been detected.
Since, in the case of the method according to the invention, the folding-nip width is measured on all the pairs of folding rollers as a sheet passes, and the folding-roller nip is then set by the associated drive at each pair of folding rollers in accordance with the measured values which have been detected, there is no need for any complicated calculation of the folding-nip widths in dependence on a thickness measurement, as is the case with the prior art known from DE-298 20 296. The method according to the invention operates without measuring the thickness of individual sheets and defective nip-width calculation. Moreover, it is possible to take account of air inclusions, the sheet compression, the roller wear and the roller contamination. Correction of the folding-nip widths is possible by the drives being activated correspondingly by a process control means, it being possible for the correction values to be entered from an operating terminal, e.g. a keyboard.
In the case of the method according to the invention, it is preferably possible for properties of a selected folding layout to be taken into account during the setting operation. Such folding layouts may be constituted, for example, by a zigzag fold or a parallel fold.
Furthermore, the measured values which have been detected may be compared with previously determined or measured reference values in order to determine roller wear or roller contamination.
The folding rollers are preferably brought into contact with one another by means of the drive, which is connected kinematically to an adjustable folding roller.
The method according to the invention can be used in a folding machine having
a plurality of pairs of folding rollers which are arranged one behind the other in a sheet-passage direction and comprise an adjustable folding roller and a stationary folding roller or two adjustable folding rollers,
each adjustable folding roller being associated a measuring device, which, as a sheet passes, detects a value corresponding to the width of the folding nip between said two folding rollers of a pair of folding rollers, and passes this value on to a process computer, and
connected kinematically to each adjustable folding roller is a drive which is controlled by said process computer on the basis of said values, detected during sheet passage, on the corresponding pair of folding rollers in order to set an optimum width of said folding nip.